His early military ventures were against members of his own sept, Dál Fiatach.
[1] In 1044 mac Eochada raided the southern Uí Néill kingdom of Brega, but was defeated, losing 200 men.
[1] In 1047 he made an alliance with Diarmait mac Maíl na mBó which helped to put pressure, from both north and south, on the kingdoms of Mide, Brega and Dublin [3] In 1056 the southern Uí Néill took 3,000 cows and 60 captives from his client Kingdom Dál nAraidi which was also raided by the Cenél nEógain in 1059.
[1] Niall's son Eochaid (died 1062) was considered co-king of Ulaid with his father.
Eochaid's son Donn Sléibe Ua hEochada (died 1091) was also a king of Ulaid, as were many of his descendants.